JP5471394B2 - Oil dilution determination device for internal combustion engine and control device for internal combustion engine - Google Patents

Description

  The present invention relates to an oil dilution determination device for an internal combustion engine and an internal combustion engine control device. In particular, the present invention relates to a measure for accurately determining the degree of oil dilution. The present invention also relates to the control of the internal combustion engine executed according to the determination result. The “oil dilution” refers to a state where engine oil stored in an oil storage section such as an oil pan is diluted with liquid fuel.

  2. Description of the Related Art In recent years, multi-fuel engines that can use a fuel of ethanol alone or a mixed fuel of ethanol and gasoline are known as internal combustion engines for automobiles (hereinafter also referred to as engines) (for example, the following patents) Reference 1).

  A vehicle equipped with this type of engine is generally called a flexible fuel vehicle (FFV), and the use of alcohol fuel improves environmental performance such as improving exhaust emissions and reducing fossil fuel consumption. Can be improved.

  By the way, in the engine, a part of the fuel injected from the injector adheres to the inner wall surface of the cylinder and mixes with the engine oil (engine oil contributing to lubrication of the inner wall surface of the cylinder) in the liquid phase. . The fuel mixed with the engine oil is scraped off from the cylinder inner wall surface as the piston reciprocates, and flows into the oil pan. If such a situation continues, oil dilution in the oil pan will proceed.

  In particular, in the case of the FFV, alcohol fuel such as ethanol having a higher boiling point than gasoline is used, and the amount of fuel injection required to obtain the same torque is larger than that of a gasoline engine (for example, target A / Because the air-fuel ratio is controlled at F = 8.9), the amount of fuel adhering to the inner wall surface of the cylinder tends to increase when the engine is cold. As a result, the progress of oil dilution is also high. That is, oil dilution is likely to proceed in a situation where a so-called cold short trip is repeated, in which a cold operation for a short time is repeated, or in a situation where a high load operation is repeated during a cold state. In particular, in a direct injection type engine that directly injects fuel into a cylinder, the distance between the injector injection hole and the inner wall surface of the cylinder is relatively short (compared to a port injection type engine). Therefore, the occurrence of oil dilution is significant.

  The fuel flowing into the oil pan as described above evaporates in the crankcase as the engine warms up, that is, as the oil temperature rises, and passes through the intake passage of the engine via a PCV (Positive Crankcase Ventilation) device. Led to. As a result, the evaporated fuel is sucked into the cylinder, causing a deviation of the air-fuel ratio with respect to the target air-fuel ratio (for example, the theoretical air-fuel ratio). In particular, in the case of ethanol alone fuel (E100 fuel), since the fuel is a single component, when the oil temperature reaches the boiling point of ethanol (about 78 ° C), the amount of fuel evaporation increases rapidly and a large amount of fuel is consumed. It will be led to the intake passage through the PCV device.

  For this reason, a means for determining the degree of oil dilution is required. In Patent Document 2 below, the difference between the air-fuel ratio correction amount before the fuel pressure is reduced and the air-fuel ratio correction amount after the fuel pressure is reduced is calculated, and whether or not oil dilution has occurred is calculated based on this value. (Actually, discrimination between the abnormality of the injector and the occurrence of oil dilution) is performed.

JP 2009-36079 A JP 2007-127076 A

  However, the variation factors of the air-fuel ratio correction amount include other factors than the oil dilution degree. The correlation between the difference in the air-fuel ratio correction amount before and after the fuel pressure is reduced and the degree of oil dilution is relatively small, and the difference in the air-fuel ratio correction amount greatly varies depending on other factors. For this reason, in the oil dilution determination operation of Patent Document 2, it is difficult to determine the degree of oil dilution with high accuracy.

  Such a problem may occur not only in the engine mounted on the FFV but also in a gasoline engine that uses only gasoline as fuel.

  The present invention has been made in view of the above points, and an object of the present invention is to determine an oil dilution determination device for an internal combustion engine that can accurately determine the degree of oil dilution and to determine the result. Another object of the present invention is to provide an internal combustion engine control device that performs a control operation.

-Principle of solving the problem-
The solution principle of the present invention devised to achieve the above object is that the correction amount of the fuel injection amount (air-fuel ratio correction amount: in the following embodiment) during low load operation and high load operation of the internal combustion engine. Focusing on the fact that the difference in the total air-fuel ratio correction amount) increases as the amount of oil dilution with fuel increases, the oil dilution determination is performed based on the difference in the fuel injection amount correction amount.

-Solution-
Specifically, the present invention relates to an oil dilution for an internal combustion engine comprising a fuel correction means for obtaining a fuel correction amount for correcting the fuel injection amount from the fuel injection valve so as to reduce the deviation of the actual air fuel ratio from the target air fuel ratio. A judgment device is assumed. Based on the difference between the fuel correction amount at the time of high load operation and the fuel correction amount at the time of low load operation, this oil dilution determination device determines the degree of dilution of the lubricating oil by the fuel in the lubricating oil reservoir. Oil dilution judgment means to perform is provided. Further, when the value obtained by subtracting the fuel correction amount during the high load operation from the fuel correction amount during the low load operation is equal to or greater than a predetermined oil dilution determination threshold, the oil dilution determination means causes the oil dilution to occur. It is configured to determine that it is present. Further, hysteresis is set between the oil dilution determination threshold for determining that the oil dilution has occurred and the oil dilution cancellation determination threshold for determining that the oil dilution has been canceled. The oil dilution determination threshold is set to a value larger than the oil dilution cancellation determination threshold.

  Here, as a concept of the determination operation by the oil dilution determination means, it is determined whether or not the lubricant is diluted with the fuel, and the degree of dilution is determined by determining the degree of dilution of the lubricant with the fuel. When the value is equal to or greater than a predetermined value, it is determined that the lubricating oil has been diluted, or the amount of dilution is recognized.

The difference between the fuel correction amount during high-load operation of the internal combustion engine and the fuel correction amount during low-load operation increases as the degree of dilution of the lubricant with the fuel increases. When the above oil dilution occurs, the amount of fuel evaporated from the lubricating oil (the fuel that diluted the lubricating oil) into the intake system depends on the degree of oil dilution regardless of the load of the internal combustion engine. While it is substantially constant (the higher the degree of oil dilution, the greater the amount of evaporated fuel introduced into the intake system), the higher the operating load of the internal combustion engine, the larger the intake air amount and the fuel injection amount. For this reason, the influence of the introduction of the evaporated fuel into the intake system on the air-fuel ratio is relatively small. On the other hand, at the time of low load operation of the internal combustion engine, since both the intake air amount and the fuel injection amount are set to be small, the influence degree of the introduction of the evaporated fuel to the intake system on the air-fuel ratio becomes relatively large. For this reason, there is a difference in the fuel correction amount between the high load operation and the low load operation of the internal combustion engine even if the amount of the evaporated fuel introduced into the intake system is the same. The higher the degree, the larger. Thus, the difference between the fuel correction amount during high load operation and the fuel correction amount during low load operation has a large correlation with the degree of oil dilution. In this means for solving the problem, the oil dilution degree can be determined with high accuracy based on the difference between the fuel correction amount during the low load operation and the fuel correction amount during the high load operation.
Specifically, as described above, when the internal combustion engine is operated at a high load, both the intake air amount and the fuel injection amount are set to be large. Therefore, the influence degree of the introduction of the evaporated fuel into the intake system on the air-fuel ratio is relatively low. Get smaller. That is, during high load operation of the internal combustion engine, the fuel correction amount is obtained as a relatively small value. On the other hand, when the internal combustion engine is operated at a low load, both the intake air amount and the fuel injection amount are set to be small, so that the influence of the introduction of the evaporated fuel into the intake system on the air-fuel ratio becomes relatively large. That is, the fuel correction amount is obtained as a relatively large value during low load operation of the internal combustion engine. This tendency becomes more prominent as the amount of evaporated fuel introduced into the intake system increases, that is, as the degree of oil dilution increases. For this reason, when the value obtained by subtracting the fuel correction amount during high load operation from the fuel correction amount during low load operation is large (when the value is equal to or greater than the oil dilution determination threshold), it is determined that oil dilution has occurred. be able to.
Further, in the present solution, hunting between the determination operation that the oil dilution has occurred and the determination that the oil dilution has been eliminated is avoided, and the determination operation can be stabilized. . In particular, the tolerances of the characteristics of the devices that make up the internal combustion engine, the tolerances of the outputs of various sensors, and fluctuations in the air-fuel ratio during operation transients (especially when alcohol fuel is used, the amount of fuel injection is large. The hunting of the determination due to the influence of the fluctuation of the fuel ratio tends to be large) can be prevented. The hysteresis is set to about 10% with respect to the fluctuation range of the fuel correction amount, for example.

  Examples of the configuration for determining oil dilution without depending on the determination operation by the oil dilution determination means described above include the following. That is, when the fuel correction amount after the warm-up of the internal combustion engine is equal to or greater than a predetermined oil dilution determination threshold value, it is determined that oil dilution has occurred without waiting for the determination operation by the oil dilution determination means. It is the structure which provided the oil dilution determination means.

  In a situation where the warm-up of the internal combustion engine has been completed and the operation has shifted to warm operation, the temperature of the lubricating oil in the lubricating oil reservoir rises above the boiling point of the fuel, causing the fuel mixed in the lubricating oil to evaporate. And introduced into the intake passage of the internal combustion engine. In this case, if the fuel correction amount is equal to or greater than a predetermined oil dilution determination threshold, it is possible to determine that the degree of oil dilution is high without calculating the difference in the air-fuel ratio correction amount during each load operation. it can. By making such a determination, a quick oil dilution determination can be made.

  Examples of the configuration for determining oil dilution when the internal combustion engine is restarted include the following. In other words, when the internal combustion engine is restarted in a state where it is determined that the oil dilution has occurred by the oil dilution determining means, the determination of the degree of oil dilution is performed based on the measured or estimated lubricating oil temperature. In this configuration, a starting oil dilution determination means is provided.

  For example, if the lubricating oil temperature is relatively high when the internal combustion engine is restarted (if it is above the boiling point of the fuel), it can be determined that the majority of the fuel that has diluted the lubricating oil has already evaporated. Even if it is determined that oil dilution has occurred before the internal combustion engine is stopped, the oil dilution determination is canceled (determined that no oil dilution has occurred) simultaneously with the restart of the internal combustion engine.

  On the contrary, if the lubricating oil temperature at the time of restarting the internal combustion engine is relatively low (less than the boiling point of the fuel), if it is determined that oil dilution has occurred before the internal combustion engine is stopped, this internal combustion engine Even at the time of restart, it can be determined that a large amount of fuel is still mixed in the lubricating oil in the lubricating oil reservoir. In this case, the oil dilution determination is not canceled and the oil dilution determination is continuously maintained. As described above, the oil dilution determination can be performed substantially simultaneously with the restart of the internal combustion engine based on the past oil dilution determination result and the lubricating oil temperature information at the time of restart of the internal combustion engine.

  Examples of the configuration for determining that the oil dilution has been eliminated without depending on the determination operation by the oil dilution determination means described above include the following. That is, when it is determined that the oil dilution has occurred by the oil dilution determining means, and the continuous operation time after the completion of warming-up of the internal combustion engine exceeds a predetermined time, the oil dilution is determined to have been eliminated. It is the structure which provided the cancellation determination means.

  Even when it is determined that the degree of oil dilution is high, the warm operation of the internal combustion engine is continued thereafter, and if the duration exceeds a predetermined time, the amount of fuel that has diluted the lubricating oil is large. Since the portion has evaporated, it is determined that the oil dilution has been eliminated. For this reason, in this solution, it is possible to perform the oil dilution cancellation determination without acquiring the air-fuel ratio correction amount at each load.

  Specific examples of the control of the internal combustion engine when it is determined that oil dilution has occurred in each of the above-described solving means include the following controls.

  First, when it is determined that oil dilution has occurred in updating the air-fuel ratio learning value for causing the air-fuel ratio feedback correction amount calculated based on the exhaust air-fuel ratio to converge within a predetermined range from a predetermined correction reference amount Is prohibited.

  In addition, when it is cold, it is determined that oil dilution has occurred when the alcohol concentration learning value is updated to converge the air-fuel ratio feedback correction amount calculated based on the exhaust air-fuel ratio within a predetermined range from the predetermined correction reference amount. If it is done, it is prohibited.

  Further, the purge operation for introducing the evaporated fuel generated in the fuel tank into the intake system is prohibited when it is determined that oil dilution has occurred.

  Further, when it is determined that oil dilution has occurred, the purge concentration learning value for learning the concentration of the purge gas for introducing the evaporated fuel generated in the fuel tank into the intake system is reset.

  When the degree of oil dilution is large, accurate calculation such as the above-described learning processes becomes difficult, and for example, the air-fuel ratio in the cylinder may greatly deviate from the stoichiometric air-fuel ratio. In order to avoid this, each of the solution means prohibits updating of the learning value.

  Further, the operation of stopping fuel injection from the fuel injection valve that is performed when a predetermined fuel cut condition is satisfied is prohibited when it is determined that oil dilution has occurred.

  If the fuel injection from the fuel injection valve is stopped while oil dilution is occurring, air-fuel ratio feedback control cannot be performed, and the air-fuel ratio in the cylinder may become overrich due to the fuel evaporated from the lubricating oil. There is sex. In order to avoid this, when oil dilution occurs, the fuel injection stop operation from the fuel injection valve is prohibited. That is, air-fuel ratio feedback control can be performed by continuing fuel injection from the fuel injection valve.

In this case, during the low load operation of the internal combustion engine, the fuel injection stop operation from the fuel injection valve is executed without prohibiting the fuel injection stop operation.

  If the fuel cut is prohibited when the load on the internal combustion engine is extremely low, an excessive increase in the temperature of the catalytic converter may occur at an early stage as the combustion state in the combustion chamber deteriorates. In order to avoid this, when the load of the internal combustion engine is extremely low, the fuel cut is executed when oil dilution occurs.

  When it is determined that oil dilution has occurred, and the fuel injection amount from the fuel injection valve is equal to or less than a predetermined amount, the air-fuel ratio for compensating for the deviation between the target air-fuel ratio and the actual air-fuel ratio The air-fuel ratio feedback control for calculating the feedback correction amount is continued.

  If the air-fuel ratio feedback control is prohibited when oil dilution occurs, it may be impossible to avoid a situation where the air-fuel ratio in the cylinder becomes overrich. In order to avoid this, when it is determined that oil dilution has occurred, if the fuel injection amount from the fuel injection valve is equal to or less than a predetermined amount, air-fuel ratio feedback control is continued.

  When the fuel injection stop operation from the fuel injection valve is prohibited, and during the deceleration operation, the intake air amount adjustment provided in the intake system is accompanied by the prohibition of the fuel injection stop operation from the fuel injection valve. The amount of intake air adjusted by the means is increased.

  That is, the intake air amount is increased in order to avoid the internal combustion engine from becoming a low load operation during the deceleration operation. As a result, it is possible to stabilize the engine speed during deceleration operation when oil dilution occurs.

  When it is determined that oil dilution has occurred during low-load operation, the increase in the fuel injection amount from the fuel injection valve is limited.

  When the internal combustion engine is in a low load operation, the required fuel injection amount is ensured by the air-fuel ratio feedback control, so that the air-fuel ratio in the cylinder is prevented from becoming overrich due to oil dilution. The increase in the fuel injection amount from the fuel injection valve is limited.

  When it is determined that oil dilution has occurred, the control range of the fuel correction amount is expanded.

  Thereby, the control range of the air-fuel ratio can be expanded. In particular, in the case of an internal combustion engine mounted on the FFV, there is a possibility that the oil dilution amount may increase significantly, so that this can be dealt with. Further, it is preferable that the control width is gradually reduced as oil dilution is eliminated.

  In the present invention, it is noted that the difference in the correction amount of the fuel injection amount (air-fuel ratio correction amount) between the low load operation and the high load operation of the internal combustion engine increases as the amount of oil dilution with fuel increases. The oil dilution determination is performed based on the difference between the correction amounts of the fuel injection amounts. For this reason, it is possible to accurately determine the degree of oil dilution.

It is a figure which shows schematic structure of the engine which concerns on embodiment, and its intake / exhaust system. It is a block diagram which shows the control system of an engine. It is a flowchart figure which shows the procedure of a fuel injection amount calculation process. It is a flowchart figure which shows the procedure of an air fuel ratio feedback process. It is a timing chart figure which shows an example of the change of a feedback correction coefficient. It is a flowchart figure which shows the procedure of an air fuel ratio learning process. It is a flowchart figure which shows the procedure of a purge density | concentration learning process. It is a flowchart figure which shows the procedure of oil dilution determination operation | movement. It is a flowchart figure which shows the procedure in the cold driving | operation of a total air fuel ratio correction amount calculation process. It is a flowchart figure which shows the procedure in the time of warm operation of the total air fuel ratio correction amount calculation processing. An example of the relationship between the engine load and the total air-fuel ratio correction amount is shown, (a) shows a case where the degree of oil dilution is large, and (b) shows a case where the degree of oil dilution is small.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied to a four-cylinder direct injection engine (internal combustion engine) mounted on an FFV will be described.

-Engine-
FIG. 1 is a diagram showing a schematic configuration of an engine 1 and its intake / exhaust system according to the present embodiment. In FIG. 1, only the configuration of one cylinder of the engine 1 is shown.

  The engine 1 according to the present embodiment includes a cylinder block 12 in which four cylinders 11 arranged in one direction are formed, and a cylinder head 13 attached to an upper portion of the cylinder block 12. Each cylinder 11 is inserted with a piston 14 in a reciprocable manner, and each piston 14 is connected to a crankshaft 16 via a connecting rod 15.

  In the intake passage 2 of the engine 1, an air cleaner 21 that filters intake air, an air flow meter 93 that outputs a signal corresponding to the amount of intake air, an intake air temperature sensor 94 that outputs a signal corresponding to the intake air temperature, and intake air A throttle valve (intake air amount adjusting means) 23 for adjusting the amount is provided. The throttle valve 23 is driven by a throttle motor 23a.

  The intake passage 2 includes an intake manifold 24 that distributes intake air to each cylinder 11 and an intake port 25 that is provided for each cylinder 11 and connected to the intake manifold 24.

On the other hand, the exhaust passage 3 is provided with an O ₂ sensor 96 that outputs a signal corresponding to the oxygen concentration in the exhaust gas, and a catalytic converter 32 for exhaust purification. The exhaust passage 3 includes an exhaust port 33 provided for each cylinder 11 and an exhaust manifold 34 that collects the exhaust ports 33.

  The cylinder head 13 is provided with an intake valve 26 for opening and closing the intake port 25 and an exhaust valve 36 for opening and closing the exhaust port 33. These valves 26 and 36 include a valve operating mechanism including a cam or the like. 17 is driven to open and close in synchronization with the crankshaft 16.

  In each cylinder 11, an injector (fuel injection valve) 4 and a spark plug 5 are attached to a cylinder head 13 so as to face the cylinder 11. When fuel is injected into each cylinder 11 by the injector 4, an air-fuel mixture is formed in the cylinder 11, and the air-fuel mixture is ignited by the spark of the spark plug 5 and burned. The combustion pressure generated by the combustion is transmitted to the piston 14 to reciprocate the piston 14. The reciprocating motion of the piston 14 is transmitted to the crankshaft 16 via the connecting rod 15, converted into a rotational motion, and taken out as an output of the engine 1.

  The exhaust gas after combustion is guided to the exhaust passage 3 and purified by the catalytic converter 32, and then released to the atmosphere through a muffler (not shown).

  As the fuel used for the engine 1, alcohol fuel such as ethanol or a mixed fuel of alcohol and gasoline can be applied.

  An oil pan (lubricating oil storage part) 18 for storing lubricating oil O is attached to the lower part 12 a of the cylinder block 12, and a crankcase 19 for accommodating the crankshaft 16 is constituted by the lower part 12 a and the oil pan 18. Has been.

  On the other hand, the fuel supply system that supplies the fuel in the fuel tank T to the injector 4 has a canister system (evaporated fuel processing device) for preventing the evaporated fuel generated in the fuel tank T from being released into the atmosphere. ) 6 is provided. The canister system 6 includes a charcoal canister 61 (hereinafter simply referred to as a canister) and a purge control valve (purge VSV) 63.

  The canister 61 accommodates an adsorbent made of activated carbon inside, and temporarily adsorbs and holds the evaporated fuel generated in the fuel tank T. The purge control valve 63 is provided in a purge pipe 62 that connects the canister 61 and the intake passage 2 (more specifically, the surge tank 27 or the upstream side of the surge tank 27). Opened when established. The evaporative fuel generated in the fuel tank T is processed by introducing (purging) the evaporative fuel adsorbed and held in the canister 61 into the intake passage 2 by opening the purge control valve 63. Yes.

  Further, a PCV device 7 for guiding blow-by gas blown into the crankcase 19 from the gap between the cylinder inner surface and the piston 14 to the intake passage 2 is provided. That is, the PCV device 7 sends blow-by gas containing nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) and the like into the cylinder 11 through the intake passage 2, and the atmosphere of this blow-by gas Prevents release into the inside.

  More specifically, the cylinder block 12 and the cylinder head 13 are provided with a blow-by gas communication passage 71 for guiding blow-by gas existing in the crankcase 19 into the cam chamber 13a. The cam chamber 13a and the intake passage 2 (more specifically, the surge tank 27 or the upstream side of the surge tank 27) are communicated with each other by a blow-by gas recirculation passage 72 that guides the blow-by gas to the intake passage 2. ing. A PCV valve 73 is provided at the upstream end of the blowby gas recirculation passage 72 to prevent backflow of the blowby gas and adjust the flow rate. By opening the PCV valve 73, blow-by gas existing in the crankcase 19 is guided to the intake passage 2. An oil separator (not shown) is disposed in the cam chamber 13a so as to remove oil mist contained in blow-by gas.

-Description of control block-
The operating state of the engine 1 configured as described above is controlled by the engine ECU 8. As shown in FIG. 2, the engine ECU 8 includes a CPU (Central Processing Unit) 81, a ROM (Read Only Memory) 82, a RAM (Random Access Memory) 83, a backup RAM 84, and the like.

  The ROM 82 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 81 executes arithmetic processing based on various control programs and maps stored in the ROM 82. The RAM 83 is a memory that temporarily stores calculation results in the CPU 81, data input from each sensor, and the like. The backup RAM 84 is a non-volatile memory that stores data to be saved when the engine 1 is stopped.

The ROM 82, CPU 81, RAM 83, and backup RAM 84 are connected to each other via a bus 87, and are connected to an external input circuit 85 and an external output circuit 86. In addition to the crank position sensor 91, the water temperature sensor 92, the air flow meter 93, the intake air temperature sensor 94, the throttle opening sensor 95, the O ₂ sensor 96, the external input circuit 85 includes an accelerator opening sensor 97, a cam angle sensor. 98, an oil temperature sensor 99 and the like are connected. Since the function of each sensor is well known, description thereof is omitted here.

  On the other hand, the external output circuit 86 is connected to a throttle motor 23a for driving the throttle valve 23, the injector 4, the igniter 51, and the like.

  The engine ECU 8 executes various controls of the engine 1 based on detection signals from the various sensors. For example, known ignition timing control of the spark plug 5, drive control of the throttle motor 23a, and the like are executed.

Further, the engine ECU 8 executes the following air-fuel ratio control (correction control of the fuel injection amount from the injector 4 based on the output of the O ₂ sensor 96). That is, the engine ECU 8 corrects the fuel injection amount of the injector 4 so that the air-fuel ratio of the air-fuel mixture introduced to each cylinder 11 is maintained at the target air-fuel ratio (for example, the theoretical air-fuel ratio). Specifically, the engine ECU 8 calculates a basic fuel injection amount that is a basis of the fuel injection amount injected into the cylinder 11 based on output signals of the crank position sensor 91 and the air flow meter 93, and the basic fuel injection amount. On the other hand, the final fuel injection amount is determined by multiplying an air-fuel ratio feedback correction coefficient, an air-fuel ratio learning value, and other coefficients described later.

-Fuel injection amount calculation process-
Next, the fuel injection amount calculation process performed according to the air-fuel ratio control will be described.

  FIG. 3 is a flowchart showing a processing procedure for calculating the fuel injection amount from the injector 4. The process shown in this flowchart is repeatedly executed at a predetermined cycle by the engine ECU 8 after the engine 1 is started.

  In this fuel injection amount calculation process, first, in step ST1, the intake air amount (detected by the air flow meter 93), the engine speed (calculated based on the output signal from the crank position sensor 91), the coolant temperature (above Each parameter indicating the current engine operating state is read, such as a water temperature sensor 92.

  In step ST2, the basic fuel injection amount QBASE is calculated based on these parameters. For example, it is calculated as the fuel injection amount for obtaining the theoretical air-fuel ratio with respect to the intake air amount.

Next, in step ST3, the final fuel injection amount QINJ is calculated by the following arithmetic expression (1).
QINJ ←
QBASE {1+ (FAF−1.0) + (KG−1.0)} K1 + K2 (1)
(K1, K2: correction coefficient)
In this calculation formula (1), “FAF” compensates for a temporary divergence of the actual air-fuel ratio with respect to the theoretical air-fuel ratio that is the target air-fuel ratio (for example, 8.9 for 100% ethanol fuel (E100 fuel)). This is an air-fuel ratio feedback correction coefficient. “KG” is an air-fuel ratio learning value for compensating for a steady divergence of the actual air-fuel ratio with respect to the stoichiometric air-fuel ratio (deviation due to a change in the characteristics of the injector 4 over time).

  The air-fuel ratio feedback correction coefficient FAF is obtained by an air-fuel ratio feedback process described later. The air-fuel ratio learning value KG is obtained by air-fuel ratio feedback processing and air-fuel ratio learning processing described later.

  When the degree of oil dilution (oil dilution with fuel) in the oil pan 18 increases and the actual air-fuel ratio tends to deviate from the stoichiometric air-fuel ratio due to an increase in the amount of fuel evaporated from the engine oil. This tendency is reflected in the air-fuel ratio feedback correction coefficient FAF and the air-fuel ratio learning value KG.

  When the final fuel injection amount QINJ is calculated in this way, this fuel injection amount calculation processing is terminated, and at the next fuel injection timing of the injector 4, fuel injection at this final fuel injection amount QINJ is performed. Thus, the valve opening period of the injector 4 is set according to the fuel pressure.

-Air-fuel ratio feedback process-
Next, the air-fuel ratio feedback process will be described with reference to FIGS.

FIG. 4 is a flowchart showing a processing procedure for calculating the feedback correction coefficient FAF. The processing shown in this flowchart is also repeatedly executed by the engine ECU 8 with a predetermined cycle after the engine 1 is started .

  In this air-fuel ratio feedback process, first, in step ST11, it is determined whether or not an execution condition for the air-fuel ratio feedback process is satisfied. As this execution condition, for example, the following three conditions can be cited.

・ Warm-up completion of engine 1 ・ Fuel cut is not executed ・ O ₂ sensor 96 is activated When at least one of these conditions is not satisfied, it is determined that the execution condition of the air-fuel ratio feedback processing is not satisfied In step ST11, NO is determined, and the process proceeds to step ST12. In step ST12, the feedback correction coefficient FAF is set to “1.0”, and then this routine is terminated. In this case, feedback control of the fuel injection amount based on the feedback correction coefficient FAF is not substantially performed. That is, the fuel injection correction amount (air-fuel ratio correction amount) by the air-fuel ratio feedback process is “0”.

On the other hand, if all the above conditions are satisfied and YES is determined in step ST11, the process proceeds to step ST13, where it is determined whether or not the output voltage Vox of the O ₂ sensor 96 is smaller than a predetermined reference voltage V1. . This reference voltage V1 is set as a value corresponding to the output voltage of the O ₂ sensor 96 when the exhaust air-fuel ratio is at the stoichiometric air-fuel ratio.

  Here, if the output voltage Vox is less than the reference voltage V1, YES is determined in step ST13, and the process proceeds to step ST14. In step ST14, assuming that the actual air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the air-fuel ratio identification flag FOX is set to “0”.

  Thereafter, the process proceeds to step ST15, where the air-fuel ratio identification flag FOX set this time is compared with the air-fuel ratio identification flag FOX (n-1) set in the previous routine.

  If these two values match and the determination is YES in step ST15, the process proceeds to step ST16, where it is determined that the state where the actual air-fuel ratio is leaner than the stoichiometric air-fuel ratio continues, and the feedback correction is performed. After adding a predetermined integral amount a (a> 0) to the coefficient FAF and setting the added value (FAF + a) as a new feedback correction coefficient FAF, this routine is terminated.

  On the other hand, if the air / fuel ratio identification flag FOX set this time is different from the air / fuel ratio identification flag FOX (n−1) set in the previous routine, if NO is determined in step ST15, the process proceeds to step ST17. Move. In this step ST17, it is determined that the actual air-fuel ratio is inverted from a richer side value to a leaner side value with respect to the stoichiometric air-fuel ratio, and a predetermined skip amount A (A> 0) is added to the feedback correction coefficient FAF. ) And the added value (FAF + A) is set as a new feedback correction coefficient FAF. The skip amount A is set to a sufficiently large value compared to the integral amount a.

On the other hand, if the output voltage Vox of the O ₂ sensor 96 is equal to or higher than the reference voltage V1, NO is determined in step ST13, and the process proceeds to step ST18. In this step ST18, assuming that the actual air-fuel ratio is richer than the theoretical air-fuel ratio, the air-fuel ratio identification flag FOX is set to “1”.

  Thereafter, the process proceeds to step ST19, where the air / fuel ratio identification flag FOX set this time is compared with the air / fuel ratio identification flag FOX (n−1) set in the previous routine.

  If these two values coincide with each other and if YES is determined in step ST19, the process proceeds to step ST20, where it is determined that the state where the actual air-fuel ratio is richer than the stoichiometric air-fuel ratio continues, and the feedback correction is performed. After subtracting a predetermined integration amount b (b> 0) from the coefficient FAF and setting the subtraction value (FAF−b) as a new feedback correction coefficient FAF, this routine is terminated.

  On the other hand, if the air-fuel ratio identification flag FOX set this time is different from the air-fuel ratio identification flag FOX (n-1) set in the previous routine, and if NO is determined in step ST19, the process proceeds to step ST21. Move. In this step ST21, it is determined that the actual air-fuel ratio is inverted from the lean side value to the rich side value based on the stoichiometric air-fuel ratio, and a predetermined skip amount B (B> 0) is determined from the feedback correction coefficient FAF. ) And the subtraction value (FAF-B) is set as a new feedback correction coefficient FAF. The skip amount B is set to a sufficiently large value as compared with the integral amount b.

After the processing of step ST17 or step ST 21 is executed, the flow proceeds to step ST22, the air-fuel ratio learning process is executed. In this air-fuel ratio learning process, the air-fuel ratio learned value KG is calculated. A specific procedure of this air-fuel ratio learning process will be described later.

  Thereafter, in step ST23, in preparation for the next air-fuel ratio feedback processing, the current air-fuel ratio identification flag FOX is stored in the RAM 83 as the air-fuel ratio identification flag FOX (n-1) as the previous value, and then this routine is terminated. To do.

  FIG. 5 is a timing chart showing an example of a change in the feedback correction coefficient FAF calculated by the above-described air-fuel ratio feedback processing.

As shown in FIG. 5, when the output voltage Vox of the O ₂ sensor 96 changes across the reference voltage V1 (skip timing in the figure), the feedback correction coefficient FAF is changed so as to be relatively large. Increase / decrease operation is performed based on the skip amounts A and B. On the other hand, during the period from when the output voltage Vox of the O ₂ sensor 96 changes over the reference voltage V1 to when it changes over the reference voltage V1 again (integration period in the figure), it changes relatively gradually. The increase / decrease operation is performed based on the integration amounts a and b.

  Here, when the actual air-fuel ratio and the stoichiometric air-fuel ratio do not have a tendency to steadily deviate, the feedback correction coefficient FAF varies around the reference value “1.0”. It will be. Therefore, the average value FAFAV of the feedback correction coefficient FAF is substantially equal to “1.0”. On the other hand, when the actual air-fuel ratio tends to steadily deviate from the stoichiometric air-fuel ratio to the rich side or the lean side due to, for example, a difference in injection characteristics in the injector 4 or fuel evaporation from engine oil, a feedback correction coefficient The FAF fluctuates around a value different from the reference value “1.0”. Therefore, the average value FAFAV of the feedback correction coefficient FAF converges to a value different from “1.0” according to the deviation tendency. Therefore, it is possible to monitor a steady divergence tendency between the actual air-fuel ratio and the theoretical air-fuel ratio based on the divergence between the reference value (“1.0”) of the feedback correction coefficient FAF and the average value FAFAV. it can. In the air-fuel ratio learning process in step ST22, an air-fuel ratio learning value KG is calculated as a parameter for monitoring this steady deviation tendency.

-Air-fuel ratio learning process-
Next, the air-fuel ratio learning process will be described with reference to the flowchart of FIG. The air-fuel ratio learning process shown in this flowchart is also repeatedly executed by the engine ECU 8 with a predetermined period after the engine 1 is started .

  In this air-fuel ratio learning process, first, in step ST31, it is determined whether or not an execution condition for the air-fuel ratio learning process is satisfied. As the execution condition, for example, the engine 1 is in a warm-up completion state.

  If the execution condition for the air-fuel ratio learning process is not satisfied, NO is determined in step ST31, and this routine is terminated.

  On the other hand, if the execution condition of the air-fuel ratio learning process is satisfied and YES is determined in step ST31, the process proceeds to step ST32, and the average value FAFAV of the feedback correction coefficient FAF is calculated by the following arithmetic expression (2). To do.

FAFAV ← (FAFB + FAF) / 2 (2)
In this equation (2), “FAFB” is the value of the feedback correction coefficient FAF when the previous skip processing, that is, the increase / decrease operation based on the skip amounts A and B is performed. That is, here, the value FAFB of the feedback correction coefficient FAF when the output voltage Vox of the O ₂ sensor 96 changes across the reference voltage V1, and then the output voltage Vox of the O ₂ sensor 96 again becomes the reference voltage V1. An arithmetic average with the value of the feedback correction coefficient FAF when the value changes over the range is calculated as the average value FAFAV.

  After the average value FAFAV of the feedback correction coefficient FAF is calculated in this way, in step ST33, the current feedback correction coefficient FAF is stored as the value FAFB at the time of the previous skip process execution in preparation for the next calculation process. .

  Next, the average value FAFAV of the feedback correction coefficient FAF is compared with predetermined values α, β (β> 1.0> α) (steps ST34, ST35).

  If the average value FAFAV of the feedback correction coefficient FAF is less than the predetermined value α, YES is determined in step ST34, and it is determined that the actual air-fuel ratio tends to deviate to the rich side from the theoretical air-fuel ratio. In step ST36, the air-fuel ratio learning value KG is learned so as to be a smaller value to compensate for this deviation tendency. That is, the predetermined value γ is subtracted from the current air-fuel ratio learned value KG, the subtracted value (KG−γ) is set as a new air-fuel ratio learned value KG, and this routine ends.

  On the other hand, if the average value FAFAV of the feedback correction coefficient FAF is greater than or equal to the predetermined value β, it is determined YES in step ST35, it is determined that the actual air-fuel ratio tends to deviate from the theoretical air-fuel ratio to the lean side, and step ST37. The air-fuel ratio learning value KG is learned so as to be a larger value to compensate for this deviation tendency. That is, the predetermined value γ is added to the current air-fuel ratio learned value KG, the added value (KG + γ) is set as a new air-fuel ratio learned value KG, and this routine ends.

  On the other hand, when the average value FAFAV of the feedback correction coefficient FAF is greater than or equal to the predetermined value α and less than the predetermined value β, the average value FAFAV fluctuates in the vicinity of the reference value “1.0”. Therefore, it is determined that the actual air-fuel ratio does not tend to deviate from the stoichiometric air-fuel ratio. In this case, NO is determined in both steps ST34 and ST35, and this routine is terminated without updating the air-fuel ratio learned value KG.

-Other controls by the engine ECU 8-
The engine ECU 8 also executes “fuel cut control”, “deceleration air amount control”, “alcohol concentration learning process”, “purge gas concentration learning process”, and “purge gas flow rate control” in addition to the various controls and processing operations described above. It is supposed to be. Since these controls and processes are well known, they will be briefly described here.

(Fuel cut control)
The fuel cut control is to stop fuel injection from the injector 4 during deceleration of the vehicle. Specifically, the depression amount of the accelerator pedal by the driver (driver) is “0” (accelerator OFF), and the engine speed is in a predetermined range (fuel cut speed (for example, 1000 rpm) or more). If the fuel cut condition is satisfied, the fuel injection from the injector 4 is stopped. Actually, after the fuel cut condition is satisfied, the fuel injection is stopped after a predetermined time has elapsed. In addition, the engine speed is reduced along with the fuel cut, and when the engine speed reaches a predetermined return speed (fuel injection return speed), fuel injection from the injector 4 is resumed.

(Deceleration air amount control)
The deceleration air amount control is the opening degree control of the throttle valve 23 during vehicle deceleration. For example, at the initial stage of the vehicle deceleration start and before the fuel cut is started, that is, while the fuel injection from the injector 4 continues, the opening of the throttle valve 23 is maintained at a predetermined opening or more to stabilize the engine speed. This is a control for achieving drivability and ensuring drivability. In addition, it is also performed as control for securing drivability by stabilizing the engine speed by securing the intake air amount when the engine is operating at the fuel injection return speed or less (at the time of fuel injection return). .

(Alcohol concentration learning process)
The alcohol concentration learning process is performed when the engine 1 is cold, and is a control for obtaining a learning value (hereinafter referred to as an alcohol concentration learning value) for compensating for a tendency of deviation of the actual air-fuel ratio from the theoretical air-fuel ratio. This is performed in the same manner as the air-fuel ratio learning process (FIG. 6) described above . For example, when using a mixed fuel containing gasoline, the degree of oil dilution increases, the fuel evaporation from the engine oil (mostly gasoline evaporation) due to increases, cold The alcohol concentration learning value is calculated as a larger value as the actual air-fuel ratio at a certain time deviates from the theoretical air-fuel ratio.

(Purge gas concentration learning process)
The purge gas concentration learning process is a control for calculating the purge gas concentration learning value, and the air-fuel ratio feedback correction coefficient based on the output of the O ₂ sensor 96 and the intake passage 2 from the canister 61 through the purge pipe 62. The purge gas concentration learning value is calculated based on the flow rate of the purge gas introduced into the. The flow rate of the purge gas is calculated based on the pressure in the canister 61 detected by a pressure sensor (not shown) and the opening degree of the purge control valve 63. By calculating the purge gas concentration learned value in this manner, the opening degree of the purge control valve 63 is adjusted based on the purge gas concentration learned value, and the purge gas flow rate is optimized.

  FIG. 7 is a flowchart showing the procedure of the purge gas concentration learning process. In this purge gas concentration learning process, first, in step ST41, the purge rate PGR (the ratio of the gas (evaporated fuel) supplied from the purge pipe 62 out of the intake air sucked into the cylinder 11 from the intake port 25) is sufficiently high. It is determined whether or not the purge rate reference value F0 indicating is exceeded. This is because a sufficient purge amount needs to be secured in order to learn the concentration of fuel vapor during purging, and if the purge rate PGR is small, the concentration of fuel vapor during purging may not be accurately recognized. It is because there is sex.

  If the purge rate PGR is less than or equal to the purge rate reference value F0, a NO determination is made in step ST41, and this routine is terminated.

  On the other hand, if the purge rate PGR is higher than the purge rate reference value F0, YES is determined in step ST41, and the process proceeds to step ST42. In this step ST42, the purge deviation correction value FAFPG is calculated by the following arithmetic expression (3).

FAFPG ←
FAFPG + {(FAFAV-1) / PGR-FAFPG} × δ (3)
Here, δ is a weight for calculating the long-term average value, and for example, a value of δ = 1/8 is set. Further, “FAFAV-1” indicates a deviation amount from the control center “1” in the average value FAFAV of the air-fuel ratio feedback coefficient FAF calculated as described above. Note that “0” is set as the initial value of the purge deviation correction value FAFPG that is initially set when the engine ECU 8 is powered on.

  Therefore, the arithmetic expression (3) obtains the long-term average value of the ratio of the deviation amount “FAFAV-1” with respect to the control center in the average value FAFAV of the air-fuel ratio feedback coefficient FAF and the purge rate PGR as the purge deviation correction value FAFPG. Will be.

  Next, in step ST43, it is determined whether or not the purge deviation correction value FAFPG is smaller than the decrease determination value B1 (<0).

  If the purge deviation correction value FAFPG is equal to or greater than the decrease determination value B1 and a NO determination is made in step ST43, the process proceeds to step ST44, and whether or not the purge deviation correction value FAFPG is greater than the increase determination value B2 (> 0). Determined.

  If the purge deviation correction value FAFPG is equal to or less than the increase determination value B2 and the determination is NO in step ST44, this routine is terminated as it is.

  On the other hand, if the purge deviation correction value FAFPG is smaller than the decrease determination value B1 and YES is determined in step ST43, the process proceeds to step ST45, where the purge concentration learning value FGPG is decreased by the fluctuation amount ε, and the purge is performed in step ST46. The deviation correction value FAFPG is cleared to zero, and this routine ends.

  On the other hand, if the purge deviation correction value FAFPG is larger than the increase determination value B2 and YES is determined in step ST44, the process proceeds to step ST47, where the purge concentration learning value FGPG is increased by the variation amount ε, and in step ST48, The purge deviation correction value FAFPG is cleared to zero, and this routine ends.

  The purge concentration learning value FGPG is not calculated for each operation region of the engine 1 but is common to all operation regions of the engine 1. The purge concentration learning value FGPG corresponds to the fuel concentration in the purged gas, but is a value relative to the control center of the air-fuel ratio.

  For example, “−0.02” is set as the decrease determination value B1, and “0.02” is set as the increase determination value B2. In this way, the purge concentration learning value FGPG is set according to the purge deviation correction value FAFPG, and is always updated.

(Purge gas flow control)
The purge gas flow rate control is a control for optimizing the purge gas flow rate by adjusting the opening degree of the purge control valve 63 (for example, adjusting the duty ratio) when a predetermined purge condition is satisfied. Further, by adjusting the fuel injection amount from the injector 4 based on the purge gas flow rate by the purge gas flow rate control, the air-fuel mixture in the cylinder 11 can be brought close to the stoichiometric air-fuel ratio.

-Oil dilution-
In the engine 1, a part of the fuel injected from the injector 4 adheres to the inner wall surface of the cylinder and mixes with the engine oil in a liquid phase state. The fuel mixed with the engine oil is scraped off from the inner wall surface of the cylinder as the piston 14 reciprocates, and flows into the oil pan 18. If such a situation continues, oil dilution in the oil pan 18 will proceed.

  In particular, since the vehicle according to the present embodiment is an FFV that uses alcohol fuel such as ethanol having a higher boiling point than gasoline, the amount of fuel adhering to the inner wall surface of the cylinder tends to increase when the engine 1 is cold. Further, in the case of alcohol fuel, the fuel injection amount for obtaining the same torque is larger than that of gasoline, so that the amount of fuel adhering to the inner wall surface of the cylinder tends to increase. As a result, the progress of oil dilution is also high.

  The fuel flowing into the oil pan 18 as described above evaporates into the crankcase 19 as the engine 1 warms up, that is, as the oil temperature rises, and is guided to the intake passage 2 via the PCV device 7. As a result, the evaporated fuel is sucked into the cylinder 11 to cause a deviation of the air-fuel ratio with respect to the target air-fuel ratio (for example, the theoretical air-fuel ratio). In particular, in the case of ethanol alone fuel (E100 fuel), since the fuel is a single component, when the oil temperature reaches the boiling point of ethanol (about 78 ° C), the amount of fuel evaporation increases rapidly and a large amount of fuel is consumed. It will be led to the intake passage 2 through the PCV device 7.

  In the engine 1, the above-described air-fuel ratio feedback processing, air-fuel ratio learning processing, and alcohol concentration learning processing are executed by the engine ECU 8 in order to reduce such an air-fuel ratio shift.

-Oil dilution judgment operation-
A feature of the present embodiment is an operation for determining the presence or absence of the oil dilution (oil dilution with fuel in the oil pan 18). In the following explanation, when the oil dilution degree is less than a predetermined amount, it is determined that oil dilution has not occurred, and when the oil dilution degree is not less than a predetermined amount, it is determined that oil dilution has occurred. An example will be described.

  An outline of this oil dilution determination operation will be described. An air-fuel ratio correction amount calculated based on the feedback correction coefficient FAF obtained by the above-described air-fuel ratio feedback processing (fuel injection correction amount resulting from the air-fuel ratio feedback processing), The air-fuel ratio learning value obtained by the air-fuel ratio learning process (corresponding to the fuel injection correction amount resulting from the air-fuel ratio learning process) and the alcohol concentration learning value obtained by the alcohol concentration learning process (caused by the alcohol concentration learning process) The total sum of the fuel correction amount and the fuel injection correction amount) is defined as “total air-fuel ratio correction amount” (operation for calculating the fuel correction amount by the fuel correction means in the present invention). Then, the total air-fuel ratio correction amount at the time of low load operation of the engine 1 is compared with this total air-fuel ratio correction amount at the time of high load operation of the engine 1, and if the difference is larger than a predetermined value, oil dilution is performed. It is determined that it has occurred (or the degree of oil dilution is large) (operation for determining the degree of dilution of lubricating oil by the oil dilution determining means in the present invention).

  When oil dilution occurs, the amount of fuel vapor introduced into the intake passage 2 generated in the oil pan 18 is substantially constant depending on the degree of oil dilution, regardless of the engine load. On the other hand, when the engine 1 is operated at a high load, the opening degree of the throttle valve 23 is large and the fuel injection amount from the injector 4 is set to be large. For this reason, during the high load operation of the engine 1, the degree of influence on the air-fuel ratio due to the introduction of the evaporated fuel into the intake passage 2 (introduction of the evaporated fuel due to oil dilution) is relatively small. The total air-fuel ratio correction amount is also obtained as a relatively small value.

  On the other hand, when the engine 1 is operated at a low load, the opening degree of the throttle valve 23 is small and the fuel injection amount from the injector 4 is also set small. For this reason, during the low load operation of the engine 1, the degree of influence on the air-fuel ratio due to the introduction of evaporated fuel into the intake passage 2 (introduction of evaporated fuel caused by oil dilution) is relatively large. The total air-fuel ratio correction amount is also obtained as a relatively large value.

  As described above, there is a difference in the total air-fuel ratio correction amount between the high load operation and the low load operation of the engine 1, and the difference is larger as the amount of evaporated fuel introduced into the intake passage 2 increases. That is, the higher the oil dilution, the larger the oil dilution. Thus, the difference between the total air-fuel ratio correction amount during high load operation of the engine 1 and the total air-fuel ratio correction amount during low load operation has a large correlation with the degree of oil dilution. In view of this point, in the present embodiment, the total air-fuel ratio correction amount during low-load operation of the engine 1 is compared with the total air-fuel ratio correction amount during high-load operation of the engine 1, and the difference is greater than a predetermined value. When it is large, it is determined that oil dilution has occurred (or the degree of oil dilution is large).

  FIG. 8 is a flowchart showing the procedure of the oil dilution determination operation. The oil dilution determination operation shown in this flowchart is repeatedly executed at a predetermined cycle by the engine ECU 8 after the engine 1 is started.

  First, in step ST51, it is determined whether or not a fuel discharge condition is satisfied. The “fuel outflow condition” here is a temperature condition in which the fuel mixed in the engine oil in the oil pan 18 evaporates into the crankcase 19. That is, when the temperature of the engine oil in the oil pan 18 is equal to or higher than the boiling point of the fuel (about 78 ° C. in the case of ethanol), the fuel spring condition is satisfied. Specifically, the determination is made based on the oil temperature detected by the oil temperature sensor 99. Further, it may be estimated from the cooling water temperature detected by the water temperature sensor 92.

  If the fuel spill condition is not satisfied and NO is determined in step ST51, this routine is terminated as it is.

  On the other hand, if the fuel outflow condition is satisfied and YES is determined in step ST51, the total air-fuel ratio correction amount for each of the high load operation and low load operation of the engine 1 is calculated. It is determined whether or not. That is, the total air-fuel ratio correction amount during high-load operation of the engine 1 (the air-fuel ratio correction amount calculated based on the feedback correction coefficient FAF obtained by the air-fuel ratio feedback process and the air-fuel ratio obtained by the air-fuel ratio learning process) (The sum of the learning value and the alcohol concentration learning value obtained by the alcohol concentration learning process) is determined, and it is determined whether or not the total air-fuel ratio correction amount during low-load operation of the engine 1 is determined. .

  More specifically, when the load factor of the engine 1 is 60% or more, the total air-fuel ratio correction amount is calculated (calculation of the total air-fuel ratio correction amount during high load operation), and the load of the engine 1 is calculated. If the total air-fuel ratio correction amount is calculated when the rate is 20% or less (calculation of the total air-fuel ratio correction amount during low load operation), a YES determination is made in step ST52.

  The load factor of the engine 1 is a value indicating the current load ratio with respect to the maximum engine load of the engine 1 and is calculated from a parameter corresponding to the intake air amount of the engine 1 and the engine speed. Further, the value of the load factor is not limited to this, but the higher the load factor that defines the calculation timing of the total air-fuel ratio correction amount during high load operation (for example, the load factor is 70% or more), The lower the load factor that defines the calculation timing of the total air-fuel ratio correction amount during low-load operation (for example, the load factor is 10% or less), the greater the difference between these total air-fuel ratio correction amounts can be obtained. Can improve the reliability.

  FIG. 9 and FIG. 10 are flowcharts showing the procedure for calculating the total air-fuel ratio correction amount. The calculation process of the total air-fuel ratio correction amount shown in this flowchart is repeatedly executed by the engine ECU 8 with a predetermined cycle after the engine 1 is started.

  First, in step ST61, it is determined whether or not the engine 1 is in a cold operation. This is determined based on the cooling water temperature detected by the water temperature sensor 92, and when the cooling water temperature is lower than a predetermined temperature (for example, 60 ° C.), it is determined that the cold operation is being performed.

  If the engine 1 is in cold operation and YES is determined in step ST61, the process proceeds to step ST62, and it is determined whether or not the operating state of the engine 1 is low load operation. This is determined by determining the load factor of the engine 1 as described above.

  And when the driving | running state of the engine 1 is low load driving | running and it determines YES in step ST62, it moves to step ST63 and acquires the alcohol concentration learning value at the time of low load driving | operation. As described above, this acquisition operation is performed in the same manner as the air-fuel ratio learning process (FIG. 6). After the alcohol concentration learning value at the time of low load operation is acquired in this way, the process proceeds to step ST64, and the low load alcohol concentration learning value acquisition flag FLAL is set to “1”.

  On the other hand, when the operation state during the cold operation of the engine 1 is not a low load operation but a NO determination is made in step ST62, the process proceeds to step ST65, and it is determined whether or not the operation state of the engine 1 is a high load operation. judge. This is also determined by determining the load factor of the engine 1 as described above.

  And when the driving | running state of the engine 1 is high load driving | running and it determines YES in step ST65, it moves to step ST66 and acquires the alcohol concentration learning value at the time of high load driving | operation. This acquisition operation is also performed in the same manner as the air-fuel ratio learning process (FIG. 6) as described above. After the alcohol concentration learning value at the time of high load operation is acquired in this way, the process proceeds to step ST67, and the high load alcohol concentration learning value acquisition flag FHAL is set to “1”.

  On the other hand, when the operation state of the engine 1 is neither low load operation nor high load operation (medium load operation), NO is determined in step ST65.

  In step ST68, it is determined whether or not both the low load alcohol concentration learned value acquisition flag FLAL and the high load alcohol concentration learned value acquisition flag FHAL are set to “1”. That is, it is determined whether or not the alcohol concentration learned value during low load operation and the alcohol concentration learned value during high load operation are both acquired.

  If only one alcohol concentration learned value is acquired, or if both alcohol concentration learned values are not acquired, NO is determined in step ST68, and this routine is terminated as it is. In this case, both the alcohol concentration learned value during low load operation and the alcohol concentration learned value during high load operation are both recognized as “0”.

  On the other hand, if both alcohol concentration learning values have been acquired, the low load alcohol concentration learning value acquisition flag FLAL and the high load alcohol concentration learning value acquisition flag FHAL are both set to “1”. A determination of YES is made in ST68 and the process proceeds to step ST69. In step ST69, the acquired alcohol concentration learned value during low load operation and the alcohol concentration learned value during high load operation are stored in the RAM 83, respectively.

  The above is the acquisition operation of the alcohol concentration learning value during the cold operation.

  On the other hand, when the engine 1 is in a warm operation, NO is determined in step ST61, and the process proceeds to step ST70 (FIG. 10). In step ST70, it is determined whether or not the operating state of the engine 1 is a low load operation.

  When the operating state of the engine 1 is low load operation and YES is determined in step ST70, the process proceeds to step ST71, and the air-fuel ratio correction amount and the air-fuel ratio learning value at the time of low load operation are acquired. This acquisition operation is performed by the air-fuel ratio feedback process (FIG. 4) and the air-fuel ratio learning process (FIG. 6) described above. After the air-fuel ratio correction amount and the air-fuel ratio learning value at the time of low load operation are acquired in this way, the process proceeds to step ST72, and the low load air-fuel ratio correction amount acquisition flag FLA / F is set to “1”.

  On the other hand, when the operation state during the warm operation of the engine 1 is not a low load operation but a NO determination is made in step ST70, the process proceeds to step ST73, where it is determined whether or not the operation state of the engine 1 is a high load operation. judge.

  If the operation state of the engine 1 is high load operation and YES is determined in step ST73, the process proceeds to step ST74, and the air-fuel ratio correction amount and the air-fuel ratio learning value at the time of high load operation are acquired. This acquisition operation is also performed by the air-fuel ratio feedback process (FIG. 4) and the air-fuel ratio learning process (FIG. 6) described above. After the air-fuel ratio correction amount and the air-fuel ratio learning value at the time of high load operation are acquired in this way, the process proceeds to step ST75, and the high load air-fuel ratio correction amount acquisition flag FHA / F is set to “1”.

  On the other hand, when the operation state of the engine 1 is neither low load operation nor high load operation (medium load operation), NO is determined in step ST73.

  In step ST76, it is determined whether or not both the low load air-fuel ratio correction amount acquisition flag FLA / F and the high load air-fuel ratio correction amount acquisition flag FHA / F are set to “1”. That is, it is determined whether or not the air-fuel ratio correction amount and air-fuel ratio learning value during low-load operation and the air-fuel ratio correction amount and air-fuel ratio learning value during high-load operation are both acquired.

  If only one of the air-fuel ratio correction amount and the air-fuel ratio learning value has been acquired, or if both of the air-fuel ratio correction amount and the air-fuel ratio learning value have not been acquired, NO is determined in step ST76, and this End the routine. In this case, the air-fuel ratio correction amount and air-fuel ratio learning value during low load operation, and the air-fuel ratio correction amount and air-fuel ratio learning value during high load operation are both recognized as “0”.

  On the other hand, when both the air-fuel ratio correction amount and the air-fuel ratio learning value are acquired, both the low load air-fuel ratio correction amount acquisition flag FLA / F and the high load air-fuel ratio correction amount acquisition flag FHA / F are both “1”. Is set to "", YES is determined in step ST76, and the process proceeds to step ST77. In step ST77, the obtained air-fuel ratio correction amount and air-fuel ratio learning value during low-load operation, and air-fuel ratio correction amount and air-fuel ratio learning value during high-load operation are stored in the RAM 83, respectively.

  The above is the operation of acquiring the air-fuel ratio correction amount and the air-fuel ratio learning value during the warm operation.

  In such total air-fuel ratio correction amount calculation processing, the total value of the alcohol concentration learned value, the air-fuel ratio correction amount, and the air-fuel ratio learned value acquired during low-load operation is the total air-fuel ratio correction during low-load operation. It is taken as a quantity. Further, the total value of the alcohol concentration learned value, the air-fuel ratio correction amount, and the air-fuel ratio learned value acquired during high-load operation is used as the total air-fuel ratio correction amount during high-load operation.

  Returning to the oil dilution determination operation of FIG. 8, if one or both of the total air-fuel ratio correction amounts are not obtained, NO determination is made in step ST52, and it is assumed that the oil dilution determination operation cannot be performed. This routine ends.

  On the other hand, the total air-fuel ratio correction amount for each of the high load operation and the low load operation of the engine 1 is calculated. If YES is determined in step ST52, the process proceeds to step ST53, where The total air-fuel ratio correction amount during high load operation is subtracted from the total air-fuel ratio correction amount, and it is determined whether this value (subtraction value) is equal to or greater than a predetermined value C (oil dilution determination threshold in the present invention). . Specifically, it is determined whether or not the subtraction value is obtained as a value of 20% or more with respect to the total air-fuel ratio correction amount during high load operation. This value is not limited to this, and is determined by experiments, simulations, or the like.

  When the subtracted value is less than the predetermined value C (for example, when the subtracted value is 10% with respect to the total air-fuel ratio correction amount during high load operation), NO determination is made in step ST53, and oil dilution occurs. Even if it has not occurred, the oil dilution determination flag is reset to “0” on the assumption that the dilution amount is small (step ST54).

  On the other hand, the subtraction value is large (for example, when this subtraction value is 30% with respect to the total air-fuel ratio correction amount during high load operation), YES is determined in step ST53, and oil dilution is occurring. Then, the oil dilution determination flag is set to “1”.

  Then, after setting the oil dilution determination flag to “1” in step ST55, an engine control operation at the time of oil dilution is executed in step ST56. A specific engine control operation executed at the time of this oil dilution will be described later.

  Note that, as described above, the oil dilution determination flag is set to “1” in step ST55, and the operation of the engine 1 is continued, and then the subtraction value is less than the predetermined value C. If NO, NO is determined in step ST53, and the oil dilution determination flag is reset to “0” on the assumption that oil dilution has not occurred or the amount of dilution is small even if it has occurred. Become.

  Here, it is determined whether or not oil dilution has occurred depending on whether or not the subtraction value is equal to or greater than a predetermined value C. However, the predetermined value C for determining that oil dilution has occurred is as follows. Alternatively, a predetermined value D for determining that no oil dilution has occurred may be set. That is, between the oil dilution determination threshold value (predetermined value C) for determining that oil dilution has occurred and the oil dilution elimination determination threshold value (predetermined value D) for determining that oil dilution has been eliminated. Is to set hysteresis. In this case, the oil dilution determination threshold value is set to be larger than the oil dilution cancellation determination threshold value. Thereby, it is possible to avoid hunting between the determination operation that the oil dilution has occurred and the determination that the oil dilution has been eliminated.

  FIG. 11 shows an example of the relationship between the engine load and the total air-fuel ratio correction amount. The left side of FIG. 11 shows the air-fuel ratio correction amount resulting from the air-fuel ratio feedback process during low load operation of the engine 1, the air-fuel ratio learning value obtained by the air-fuel ratio learning process, and the alcohol concentration learning process. The magnitude of the total air-fuel ratio correction amount, which is the sum of the obtained alcohol concentration learning value, is shown. On the other hand, the right side of FIG. 11 shows the air-fuel ratio correction amount resulting from the air-fuel ratio feedback process at the time of high load operation of the engine 1, the air-fuel ratio learning value obtained by the air-fuel ratio learning process, and the alcohol concentration learning process. The amount of the total air-fuel ratio correction amount that is the sum of the alcohol concentration learning value obtained by the above is shown. Thus, there is a difference in the air-fuel ratio correction amount between the low load operation and the high load operation even if the degree of oil dilution is the same. This difference is obtained as a larger value as the degree of oil dilution increases. FIG. 11 (a) shows the total air-fuel ratio correction amount at each operation when the degree of oil dilution is large (when YES is determined in step ST53), and FIG. 11 (b) shows the degree of oil dilution. The total air-fuel ratio correction amount at the time of each operation when it is small (when NO is determined at step ST53) is shown.

  As described above, in the present embodiment, the total amount of the evaporated fuel (fuel evaporated from the engine oil) to the intake system is the same during the high load operation and the low load operation of the engine 1. Note that there is a difference in the air-fuel ratio correction amount, and that the difference becomes larger as the oil dilution becomes higher, that is, the total air-fuel ratio correction amount in the high load operation and the total air ratio in the low load operation. Focusing on the fact that the difference from the fuel ratio correction amount has a large correlation with the degree of oil dilution, the oil dilution is based on the difference between the total air fuel ratio correction amount during high load operation and the total air fuel ratio correction amount during low load operation. The degree can be determined with high accuracy.

  Further, according to the oil dilution determination operation of the present embodiment, even if new fuel is supplied to the fuel tank T and the fuel type is changed in a state where the degree of oil dilution is high, the current oil The degree of dilution can be accurately determined. For example, even when ethanol dilution fuel (E100 fuel) is used, the degree of oil dilution increases, and then a mixed fuel of ethanol and gasoline (for example, E50 fuel) is supplied to the fuel tank T. It is possible to accurately determine the degree of oil dilution.

-Other oil dilution judgment-
In addition to performing the oil dilution determination based on the difference between the total air-fuel ratio correction amount during the high load operation of the engine 1 and the total air-fuel ratio correction amount during the low load operation as described above, The oil dilution determination can be performed also by the operation described below. In addition, an operation for canceling the oil dilution determination is also performed. This will be specifically described below.

(Dilution judgment during warm operation)
When the warm-up of the engine 1 is completed and the operation is shifted to the warm operation, the temperature of the engine oil in the oil pan 18 rises above the boiling point of the fuel, so that the fuel mixed in the engine oil becomes crankcase 19. Evaporates in. The evaporated fuel is introduced into the intake passage 2 via the PCV device 7. In this case, when the total air-fuel ratio correction amount (total air-fuel ratio correction amount for warm operation) is equal to or greater than a predetermined oil dilution determination threshold value, it is determined that the degree of oil dilution is high regardless of the load state of the engine 1. I have to. This oil dilution determination threshold is determined by experiment, simulation, or the like.

  For example, in the situation where the cooling water temperature detected by the water temperature sensor 92 exceeds 60 ° C. or the oil temperature detected by the oil temperature sensor 99 exceeds 60 ° C., the total air-fuel ratio correction amount Is equal to or greater than the oil dilution determination threshold value, it is determined that the degree of oil dilution is high (oil dilution determination operation by the oil dilution determination means in the present invention).

  According to this, it is possible to determine that the degree of oil dilution is high without waiting for acquisition of the total air-fuel ratio correction amount during low-load operation and the total air-fuel ratio correction amount during high-load operation. In other words, even if the total air-fuel ratio correction amount cannot be acquired for each load, it can be determined that the degree of oil dilution is high, and a quick determination process can be realized.

(Dilution judgment at engine restart)
After the oil dilution determination (oil dilution determination based on the difference in the total air-fuel ratio correction amount or the oil dilution determination during warm operation) is performed as described above, the engine 1 is stopped and then restarted. The oil dilution determination is performed according to the oil temperature or the like (oil dilution determination operation by the restart-time oil dilution determination means in the present invention).

  That is, when the engine 1 is stopped, the oil dilution determination flag is stored in the backup RAM 84, and the information is read from the backup RAM 84 when the engine 1 is restarted thereafter. Further, the oil temperature information at the time of restart of the engine 1 is acquired, and the read-out oil dilution determination information is continuously used or the determination information is reset. The oil temperature information may be an oil temperature signal detected by the oil temperature sensor 99, or information obtained by estimating the oil temperature from the cooling water temperature detected by the water temperature sensor 92.

  For example, if it is determined that the oil temperature is relatively high and most of the fuel that has diluted the oil has evaporated, it is assumed that the oil dilution determination flag before engine stop is set to “1”. At the same time as restarting the engine 1, the oil dilution determination flag is reset to “0”.

  Conversely, when it is determined that the oil temperature is relatively low and the engine oil in the oil pan 18 still contains a large amount of fuel, the oil dilution determination flag before engine stop is set to “1”. In the case where it has been set, the oil dilution determination flag is held at “1” even after the engine 1 is restarted.

  According to this, based on the past oil dilution determination result (before the engine 1 is stopped) and the oil temperature information when the engine 1 is restarted, the oil dilution determination can be performed substantially simultaneously with the restart of the engine 1. It becomes possible.

(Oil dilution release judgment)
The fuel mixed in the engine oil evaporates after the warm-up of the engine 1 is completed, and when the engine 1 is continuously operated, most of the fuel evaporates and the oil dilution is eliminated. .

  In view of this point, if it is determined that the degree of oil dilution is high and the operation continuation time after completion of warm-up of the engine 1 exceeds a predetermined time (for example, 30 minutes), the oil dilution amount is temporarily set. Even if the maximum amount is reached, most of the fuel that has diluted the oil is evaporated, and it is determined that the oil dilution has been eliminated. That is, without obtaining the total air-fuel ratio correction amount at each load, the oil dilution release determination is performed and the oil dilution determination flag is reset to “0” (the oil dilution cancellation determination means in the present invention refers to the oil dilution determination means). Dilution elimination judgment operation).

  The oil dilution determination and the oil dilution release determination described above are not necessarily performed only for the engine 1 for which the oil dilution determination is performed based on the difference in the total air-fuel ratio correction amount described above.

-Engine control during oil dilution-
Next, engine control at the time of occurrence of oil dilution performed in step ST56 of FIG. 8 will be described. In the following, a plurality of controls are listed as engine controls when oil dilution occurs, but any of these controls may be performed alone or in parallel.

(Hold the air-fuel ratio learning value)
First, as the engine control when oil dilution occurs, the air-fuel ratio learning value is held. That is, when the oil dilution occurs, the current air-fuel ratio learning value is prohibited by holding the air-fuel ratio learning process.

  This is because, when the degree of oil dilution is large, it is difficult to accurately calculate the air-fuel ratio learning value by the air-fuel ratio learning process, and a malfunction caused by calculating an incorrect air-fuel ratio learning value (for example, the air-fuel ratio in the cylinder 11). This is to avoid a large deviation from the stoichiometric air-fuel ratio.

(Hold alcohol concentration learning value)
Further, as the engine control when oil dilution occurs, the alcohol concentration learned value is held. In other words, the current alcohol concentration learning value is held by holding the alcohol concentration learning process when oil dilution occurs.

  This is because when the degree of oil dilution is large, it is difficult to calculate an accurate alcohol concentration learning value by the alcohol concentration learning process, and a malfunction caused by calculating an incorrect alcohol concentration learning value (for example, the air-fuel ratio in the cylinder 11). This is to avoid a large deviation from the stoichiometric air-fuel ratio.

(Purge control prohibited)
As engine control when oil dilution occurs, prohibition of purge control can be mentioned. That is, the purge control valve 63 in the canister system 6 is maintained in the fully closed state, and the introduction (purging) of the evaporated fuel adsorbed and held in the canister 61 into the intake passage 2 is prohibited.

  This is because when the degree of oil dilution is large, it becomes difficult to accurately measure the purge gas flow rate (the amount of fuel vapor introduced into the intake passage 2), and the air-fuel ratio of the air-fuel mixture in the cylinder 11 becomes less than the stoichiometric air-fuel ratio. This is to avoid this because it may deviate greatly and may lead to deterioration of drivability.

(Purge concentration learning value hold)
An example of engine control when oil dilution occurs is holding the purge concentration learned value. In other words, the current purge concentration learning value is held by holding the purge concentration learning process when oil dilution occurs.

  This is because when the degree of oil dilution is large, it is difficult to accurately calculate the purge concentration learning value by the purge concentration learning process, and a problem caused by calculating an incorrect purge concentration learning value is avoided.

(Prohibition of fuel cut)
An example of engine control when oil dilution occurs is to prohibit fuel cut. As described above, while the vehicle is decelerating, fuel cut control for stopping fuel injection from the injector 4 is basically executed. When oil dilution occurs, this fuel cut is prohibited and fuel injection from the injector 4 is performed. To continue.

  The reason for this is to avoid the possibility that the air-fuel ratio feedback control cannot be performed by the fuel cut and the air-fuel ratio in the cylinder 11 becomes overrich due to the fuel evaporated from the engine oil (engine When there is a lot of fuel evaporated from oil). Further, if the fuel cut is performed in a state where the fuel evaporated from the engine oil is introduced into the cylinder 11, misfire occurs in the combustion chamber, and unburned gas is burned in the exhaust system, and the catalytic converter 32. This is to avoid the excessive increase in the temperature of the engine (if the amount of evaporated fuel from the engine oil is small).

  However, when the load on the engine 1 is extremely low (for example, when the load factor is less than 10%), the fuel injection from the injector 4 is stopped without prohibiting fuel cut as engine control at the time of oil dilution. ing.

  The reason is that if the fuel cut is prohibited when the load on the engine 1 is extremely low, that is, if the fuel injection from the injector 4 is continued, the temperature of the catalytic converter 32 becomes worse as the combustion state in the combustion chamber deteriorates. There is a possibility that an excessive increase will occur early. In order to avoid this, when the load of the engine 1 is extremely low and the oil dilution occurs, the fuel cut is executed.

(Continuation of air-fuel ratio feedback control)
As engine control at the time of oil dilution occurrence, when the fuel injection amount from the injector 4 is equal to or less than a predetermined amount, the air-fuel ratio feedback control for calculating the air-fuel ratio feedback correction amount may be continued.

  If the air-fuel ratio feedback control is prohibited when oil dilution occurs, the air-fuel ratio in the cylinder 11 may become overrich. In order to avoid this, when it is determined that the oil dilution is occurring, if the fuel injection amount from the injector 4 is equal to or less than the predetermined amount, the air-fuel ratio feedback control is continued and the air in the cylinder 11 is emptied. The fuel ratio is stabilized near the stoichiometric air-fuel ratio.

(Intake increase during deceleration operation)
As described above, when the fuel injection stop operation from the injector 4 is prohibited as the engine control when the oil dilution occurs, when the vehicle is decelerating, the throttle valve is accompanied by the prohibition of the fuel injection stop operation. It is possible to increase the intake air amount by setting the opening degree of 23 large.

  That is, the intake air amount is increased in order to avoid the engine 1 becoming a low load operation during the deceleration operation. Thereby, it is possible to stabilize the engine speed during the deceleration operation when oil dilution occurs, and to ensure drivability.

(Injection amount restriction during low-load operation)
As engine control at the time of oil dilution occurrence, when it is determined that oil dilution has occurred during low-load operation of the engine 1, an increase in the fuel injection amount from the injector 4 is limited.

  When the engine 1 is in a low load operation, the required fuel injection amount is ensured by the air-fuel ratio feedback process described above. For this reason, the increase in the fuel injection amount from the injector 4 is limited in order to prevent the air-fuel ratio in the cylinder 11 from becoming over-rich due to oil dilution. For example, 10% reduction correction is performed with respect to the normal fuel correction amount of the injector 4.

(Expansion of control range of fuel correction amount)
As engine control at the time of oil dilution occurrence, when it is determined that oil dilution has occurred, the control range of the total air-fuel ratio correction amount can be increased.

  As a result, the control range of the air-fuel ratio can be expanded, and in particular, in the case of the engine 1 mounted on the FFV, the oil dilution amount may increase significantly. Can do. The control width is gradually reduced as oil dilution is eliminated.

  Each engine control at the time of oil dilution described above is not necessarily executed when it is determined that the degree of oil dilution is large by the oil dilution determination described above. That is, the engine control can be performed even when it is determined that the degree of oil dilution is large by other oil dilution determinations (for example, well-known oil dilution determinations). In other words, each engine control at the time of oil dilution described above is not restricted by the oil dilution determination operation.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to the automobile four-cylinder engine 1 has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Also, the number of cylinders and the engine type (separate types such as in-line type, V type, and horizontally opposed type) are not particularly limited.

In the above embodiment, the air-fuel ratio feedback process and the air-fuel ratio learning process are performed based on the output of the O ₂ sensor 96 provided on the upstream side of the catalytic converter 32. The present invention is not limited to this, and an A / F sensor may be provided on the upstream side of the catalytic converter 32, and air-fuel ratio feedback processing and air-fuel ratio learning processing may be performed based on the output of the A / F sensor. Further, an O ₂ sensor and an A / F sensor may be used in combination.

  Further, in the above embodiment, the case where the present invention is applied to the direct injection type engine 1 has been described. The present invention is not limited to this, and can be applied to a port injection type engine and an engine including both a port injection type and an in-cylinder direct injection type injector.

  In the above embodiment, the case where the present invention is applied to the engine 1 mounted on the FFV, that is, the engine 1 that uses alcohol fuel or a mixed fuel of alcohol and gasoline has been described. The present invention is not limited to this, and can also be applied to an engine using gasoline alone.

  In the above embodiment, the total air-fuel ratio correction amount is calculated as the sum of the air-fuel ratio correction amount, the air-fuel ratio learning value, and the alcohol concentration learning value. However, the total air-fuel ratio correction amount is the sum of only the air-fuel ratio correction amount and the air-fuel ratio learning value. The fuel ratio correction amount may be calculated. That is, the alcohol concentration learning value acquired during the cold operation may be excluded from the total air-fuel ratio correction amount. This is because, for example, in the case of ethanol alone fuel (E100 fuel), fuel evaporation from engine oil hardly occurs during cold operation, and there is almost a difference in the alcohol concentration learning value between high load operation and low load operation. Because there is no. In this case, for example, when the coolant temperature and the oil temperature both exceed 60 ° C., the total air-fuel ratio correction amount is calculated.

  The present invention is applicable to an operation for determining whether or not oil is diluted with fuel in an oil pan of an engine mounted on the FFV.

1 Engine 18 Oil pan (lubricating oil reservoir)
23 Throttle valve (intake air volume adjusting means)
4 Injector (fuel injection valve)
8 Engine ECU
92 Water temperature sensor 96 O ₂ sensor O Engine oil (lubricating oil)

Claims (14)

In an oil dilution determination apparatus for an internal combustion engine comprising fuel correction means for obtaining a fuel correction amount for correcting a fuel injection amount from a fuel injection valve so as to reduce a deviation of an actual air-fuel ratio with respect to a target air-fuel ratio,
Oil dilution determination means for determining the degree of dilution of the lubricating oil by the fuel in the lubricating oil reservoir based on the difference between the fuel correction amount during high load operation and the fuel correction amount during low load operation. And
The oil dilution determining means determines that oil dilution has occurred when a value obtained by subtracting the fuel correction amount during high load operation from a fuel correction amount during low load operation is equal to or greater than a predetermined oil dilution determination threshold. It comes to judge,
Hysteresis is set between the oil dilution determination threshold for determining that the oil dilution has occurred and the oil dilution cancellation determination threshold for determining that the oil dilution has been canceled,
An oil dilution determination apparatus for an internal combustion engine, wherein an oil dilution determination threshold value is set to be larger than the oil dilution elimination determination threshold value . The oil dilution determination apparatus for an internal combustion engine according to claim 1,
If the fuel correction amount after completion of warm-up of the internal combustion engine is greater than or equal to a predetermined oil dilution determination threshold, the oil that determines that oil dilution has occurred without waiting for a determination operation by the oil dilution determination means An oil dilution determination device for an internal combustion engine, characterized in that dilution determination means is provided. The oil dilution determination apparatus for an internal combustion engine according to claim 1 or 2,
When the internal combustion engine is restarted in a state where it is determined that the oil dilution has occurred by the oil dilution determination means, at the time of restart for determining the degree of oil dilution based on the measured or estimated lubricating oil temperature An oil dilution determination device for an internal combustion engine, characterized in that an oil dilution determination means is provided. In the internal combustion engine oil dilution determination apparatus according to claim 1, 2, or 3,
After the oil dilution determining means determines that oil dilution has occurred, if the continuous operation time after completion of warming up of the internal combustion engine exceeds a predetermined time, the oil dilution is determined to have been canceled. An oil dilution determination apparatus for an internal combustion engine, characterized in that a determination means is provided. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
When it is determined that oil dilution has occurred, the update of the air-fuel ratio learning value for converging the air-fuel ratio feedback correction amount calculated based on the exhaust air-fuel ratio within a predetermined range from the predetermined correction reference amount An internal combustion engine control device configured to be prohibited. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
When it is cold, it is determined that the oil dilution is occurring when the alcohol concentration learning value is updated to converge the air-fuel ratio feedback correction amount calculated based on the exhaust air-fuel ratio within a predetermined range from the predetermined correction reference amount. An internal combustion engine control device characterized in that it is prohibited in some cases. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
An internal combustion engine controller configured to prohibit a purge operation for introducing evaporated fuel generated in a fuel tank into an intake system when it is determined that oil dilution has occurred. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
When it is determined that oil dilution has occurred, the purge concentration learning value for learning the concentration of the purge gas for introducing the evaporated fuel generated in the fuel tank into the intake system is reset. An internal combustion engine control device. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
An internal combustion engine configured to prohibit a fuel injection stop operation from a fuel injection valve, which is performed when a predetermined fuel cut condition is satisfied, when it is determined that oil dilution occurs. Control device. The internal combustion engine control apparatus according to claim 9,
An internal combustion engine controller configured to execute a fuel injection stop operation from a fuel injection valve without prohibiting a fuel injection stop operation during low load operation. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
When it is determined that oil dilution has occurred, and the fuel injection amount from the fuel injection valve is less than or equal to a predetermined amount, air-fuel ratio feedback correction for compensating for the difference between the target air-fuel ratio and the actual air-fuel ratio An internal combustion engine control device configured to continue air-fuel ratio feedback control for calculating an amount. The internal combustion engine control apparatus according to claim 9,
When the vehicle is decelerating, the intake air amount adjusted by the intake air amount adjusting means provided in the intake system is increased with the prohibition of the fuel injection stop operation from the fuel injection valve. An internal combustion engine control device. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
An internal combustion engine controller configured to limit an increase in fuel injection amount from a fuel injection valve when it is determined that oil dilution has occurred during low-load operation. An internal combustion engine control device that controls an internal combustion engine based on an oil dilution determination result by the oil dilution determination device for an internal combustion engine according to any one of claims 1 to 4,
An internal combustion engine controller configured to expand the control range of the fuel correction amount when it is determined that oil dilution has occurred.

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